The present invention relates generally to control systems for stepper motors, and more particularly, to a two-phase stepping motor gauge control system.
Analog instrumentation remains the most widely used and preferred method of displaying automobile data to the driver. This is due to their simple function and ability to be adapted to many different styles. Even expensive automobile models that essentially have an unlimited instrumentation budget commonly choose analog gauges. Future requirements for instruments will unquestionably include analog gauges.
Although air core gauges have enjoyed wide usage for many, many years, they continue to enjoy significant usage in the age of electronics because they provide certain advantages that newer electronic readouts have not yet been able to achieve. Perhaps, most significant of these advantages are cost, durability, and ease of reading.
An air core gauge can be fabricated in a cost-effective manner. Once an air core gauge has been installed and found to be operating properly, it should provide reliable service for the life of the vehicle in normal circumstances. Because an air core gauge uses a pointer to indicate its reading, the driver can quickly see if a reading is normal or abnormal.
An electronic gauge that comprises a digital readout is generally more costly, and the value of the parameter which it displays may require interpretation by the driver in order to determine if the reading is normal or abnormal. While the latter attribute of a digital electronic readout may not always be true in the case of a digital speedometer, a digital tachometer, or a digital fuel level gauge, it is often true in the case of other readouts.
Stepper motor gauges are being used increasingly in vehicle displays instead of traditional air core gauges because they exhibit improved accuracy, linearity, lower power consumption and they are easier to drive from a microprocessor. Unfortunately, typical control of a two-phase stepper motor coil requires the use of two control lines.
In some stepper motors, the geometry of the motor core provides two natural stable or detent points for the two pole rotor. Adjacent points define a full motor step. These points are important when considering the behavior of the motor when a gauge is powered down. When power is removed from the motor, the rotor approaches equilibrium to the closest one of the two detent points and is used as a rest point. Other stepper motors are designed to minimize the stable detent effect, and when power is removed from the motor the rotor remains stationary due to friction. In this case, any point may be selected as a rest point.
The disadvantages associated with these conventional motor control techniques have made it apparent that a new technique for two-phase stepper motor control is needed. The new technique should allow the control of a conventional two-phase motor coil using only one control signal. Additionally, the new technique should require low actual current to maintain gauge position. The present invention is directed to these ends.
It is, therefore, an object of the invention to provide an improved and reliable two-phase stepping motor gauge control system. Another object of the invention is to allow the control of a conventional two-phase motor coil using only one control signal.
In accordance with the objects of this invention, a two-phase stepping motor gauge control system is provided. In one embodiment of the invention, a method for controlling a two-phase stepping motor gauge for an instrument cluster includes the steps of: providing a two-phase motor for displaying information to a driver, determining a desired position of the two phase motor at a rate and in a manner consistent with an intended application; updating a waveform to the input of a first inverter coupled to one of the motor coils; integrating the waveform using a first and second inverter to energize one of the motor coils.
The present invention thus achieves an improved two-phase stepping motor gauge control system. The present invention is advantageous in that low actual current is required to maintain gauge position.
Additional advantages and features of the present invention will become apparent from the description that follows, and may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims, taken in conjunction with the accompanying drawings.